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What do "cork screwing" and "pushing air" have to do with propellers?
I am in the middle of my PPL(A) theory and I am experiencing a mental breakdown studying propellers. Until yesterday I was happily living in my ideal world where I was sure I really understood all the relevant aspects and details about how propellers are designed and actually work.
Then today I stumbled upon a webpage that destroyed all my self-confidence with just 2 out of 3 sentences:

Firstly, the shape of the propeller is such that it cork screws through the air. The cork screw motion pulls the propeller and the plane through the air

Ok, I thought this was just a huge misconception. I thought propeller blades, as aerofoils, generated Lift and Induced Drag, which we consider as Torque and Thrust in relation to the rotational plane for a number of reasons. All this having nothing to do with "cork screwing into the air" for the same reason why a wing doesn't go up because it cork screw itself into the airflow. It simply generates Lift. Is there something I am missing?

Secondly, the propeller spins at high speeds pushing air back and thus pushing the plane forward. The more air that is pushed back the more the plane is pushed forward

Ok.. no. I really thought this was how a jet engine works, not a propeller. Again, I must be missing a LOT.

Thirdly, [...] the blades are actually wings that spin around. The curved surface of the blades face the front of the plane and this creates a low pressure region in front of the plane sucking it forward

Oh finally!
Now, since I believed only the 3rd point made sense, are the first 2 described effects real?

Welcome to avaition.stackexchange.com!

If you are suffering from a mental breakdown, you should see a qualified mental health practitioner.

Cork is just a very dense form of air. Rotating corkscrew creates lift and pushes itself forwards ;-)

I really thought this was how a jet engine works, not a propeller Actually, both work the same way in principle. If you think of them as a black box, both accelerate air. Jets accelerate little air by much while propellers accelerate much air by a little.

If you change your perspective from the blades to the air, which, if you put tracer smoke around, you would see the corkscrew effect of the air it may help

Is it more intuitive to you to visualise how a helicopter flies? In that case, each blade of the rotor is effectively a rotating wing. Now see the Bell Boeing V-22 Osprey (wikipedia). It has two helicopter rotors which also vector by 90 degrees to become propellers.

Helicopter blades, yes. Because they utilize AoA much more than they use airfoiling, just like everything else does that points its nose into the sky to climb.

All three sentences make sense to me.

Firstly, the shape of the propeller is such that it cork screws
through the air. The cork screw motion pulls the propeller and the
plane through the air

The cork screw reference here is to say that with every revolution, the propeller advances through the air, pushing more air behind it.
A nice visualisation of that occurs when the propeller tip vortices are causing condensation. See the cork screw?

 Photo: Ron Kellenaers / Airlines.net Source

Secondly, the propeller spins at high speeds pushing air back and thus
pushing the plane forward. The more air that is pushed back the more
the plane is pushed forward

That is Newtons third law in action (or reaction?). By accelerating air backwards, the propeller (and the plane attached to it) must be forced forwards.

Thirdly, [...] the blades are actually wings that spin around. The
curved surface of the blades face the front of the plane and this
creates a low pressure region in front of the plane sucking it forward

Yup, that is how a propeller accelerates the air backwards, just like a wing accelerates air downwards.

Yes, of course the forward motion of a propeller resembles a corkscrew, but I think this is simply an effect caused by rotation + forward motion, it is definitely not the main reason why a propeller pulls an aircraft (I don't think it even contributes at all). As for the 3rd law, yes I think there must be an effect, but negligible, or maybe just a secondary contributing factor. I think the main principle pulling an aircraft is the last one.

The three sentence are all correct, they are just different ways for looking at the same thing. The 3rd law effect in not negligible at all, it accounts for 100% of the thrust. And so does the lift force on the wing.  The pressure distribution over the wing causes the air to accelerate backwards. They are two sides of the same coin.

Ok, so please help me: if I understand correctly, the sentence "The cork screw motion pulls the propeller and the plane through the air" actually means "The cork screw motion provides airflow to the blade element, which, thank to the lift generated by its angle of attack  pulls the propeller and the plane through the air"? or maybe I still dont get it

Yes, that is a good way of looking at. Suppose we had a propulsion system that consists of a scoop that would throw air backwards. That would work, but we would have to reposition the scoop in the forward position before we could thrust the next parcel of air backwards. The propeller doesn't have that problem; it corkscrews its way through the air, making sure there is always a fresh supply of static air to kick backwards.

My bad, I thought the article was really talking about 3 distinct effects, now it makes sense thanks

You're welcome, glad I could help! Can you include a link to the article in your question?

of course: http://www.dynamicscience.com.au/tester/solutions1/flight/demonstration%20newtons%20law%20propeller.htm

"Firstly, the shape of the propeller is such that it cork screws through the air. The cork screw motion pulls the propeller and the plane through the air" This sentence is misleading: The propeller pushes air downwards relatively to its chord, as any airfoil does. The fact that there is a rotation makes it appear like an helix. Exactly like the wingtips of an aircraft spinning around its longitudinal axis would also draw an helix. The helix has no particular effect or signification for lift. "The cork screw motion pulls the propeller" is irrelevant, and for me it's a misunderstanding.

A corkscrew is just an inclined ramp going around in a circle.  A propeller is just a wing that wants to fly straight ahead but is forced to go in a circle due to it's root connection to an axle.  They're both going up a ramp so to speak. so to the extent that the analogy is useful, it works for the purpose of visualization.

When I first saw that photo, I thought the corkscrews were photoshopped in.

@JohnK Nitpick: a corkscrew is an inclined plane going in a helix. Unless you're in an M.C Escher painting, making a corkscrew out of an inclined plane going in a circle is rather difficult.

@mins I agree, IMHO in this form it may be a little misleading

"The curved surface of the blades face the front of the plane and this creates a low pressure region in front of the plane sucking it forward" I think that quote from the question is misleading and needs to be addressed. The front face or upper face of an aerofoil does not have to be curved. Curved aerofoils are more efficient but it is not a necessary condition for thrust or lift.

@user815129: I've elaborated on how this is misleading in a true answer, it was also a good opportunity to clarify other points.

The "corkscrew" motion is important for understanding how propeller blade pitch, RPM, airspeed, and thrust are related. Consider a fixed-pitch prop for simplicity. In one revolution, the "corkscrew" moves a fixed distance forwards. If the aircraft moves the same distance forwards in the same time, the propeller thrust will be zero. If the prop RPM is higher, the thrust will be positive, and if it is lower it will be negative and decelerates the plane. The same applies to a fixed speed prop, where changing the blade pitch matches the "size" of the corkscrew to the air speed and thrust .

Firstly, any new readings or points of view should be carefully reviewed and compared with current information to avoid these lapses in confidence.
As Delta Lima pointed out, "corkscrewing" more aptly describes the combined motion path of the the propeller and the aircraft from a third frame of reference.  A good analogy would be "the earth corkscrews around the sun as both revolve around the galaxy".  This should not shatter our view that we are safely orbiting our sun.
The propeller indeed is twisted a bit due to the differences in angular rotation speed (of the propeller) relative to the forward motion of the plane (which helps optimize the AOA of more of the prop to the relative wind).  But from the aircraft reference the prop always rotates around its engine.
The second and third points (about moving air and creating suction in front, really pull and push) are consistent with lifting theory of wings turned sideways, that is: the bottom of the wing pushes air down, causing the wing to go up.  The cambered top of the wing creates low pressure, pulling the wing up.
The two work together.  As a final note, distinguishing props from simple action/reaction mass movers is correct.  It is their wing-like lifting method of propulsion that gives them an efficiency advantage.

The Frame of Reference point is excellent.  Using the pilot's seat as a fixed datum, the props are pushing the entire world backward !

Plus a propeller still generates thrust when the aircraft not moving (i.e. wheel brakes on), so the idea that the thrust is due to the corkscrew motion cannot be correct.

@DavidWaterworth Even when the aircraft is motionless with respect to the ground, the propeller is still "corkscrewing" with respect to the air that it's pushing.

Well, the way a propeller works is a little bit like a corkscrew. There are several similarities:

Both machines penetrate a surrounding medium—a propeller penetrates air, and a corkscrew penetrates a cork.
Both machines move in a helical path, as seen by an outside observer.
Both machines produce a force on the surrounding medium which is approximately perpendicular to their direction of motion.

However, there are some important differences, too.
Cork is a solid, so when a corkscrew penetrates a cork, the angle of attack of the corkscrew is almost exactly zero. Air is a fluid, so it slips out of the way of the propeller, to a certain extent. As a result, the angle of attack of a propeller through air can be substantially different from zero.
Since cork is a solid, a corkscrew doesn't have to have any special shape in order to lift the cork out of the bottle. Since air is a fluid, propeller blades have to be specially designed to produce a lot of lift.
And since cork is a solid, the user of a corkscrew can screw it in slowly, rest for a while, and then pull the cork out. Since air is a fluid, propellers can't be used that way. Propellers have to spin fast in order to produce thrust.
I would say that overall, the notion that a propeller "cork screws through the air" is not very accurate. Your prior understanding of how a propeller works is probably more accurate.
That said, the next paragraph that you quote—

Secondly, the propeller spins at high speeds pushing air back and thus pushing the plane forward. The more air that is pushed back the more the plane is pushed forward.

—is 100% accurate. All aircraft engines (and all spacecraft engines!) produce equal amounts of thrust and backwash. In order for an aircraft (or spacecraft) to push itself forwards, it must produce an equal push backwards on the surrounding air (or, in the case of a rocket engine, on its own exhaust).

"Corkscrew" the verb has a different meaning than "corkscrew" the noun.

@nick012000 That's true, but I get the impression that the paragraph about "cork screw[ing] through the air" was intended to make a comparison to an actual corkscrew. If we take "corkscrew" as meaning merely "to move in a helical path," then the paragraph is merely stating that the propeller moves in a helical path and generates a force, but fails to say anything about how or why any force is generated.

@TerranSwett "Move in a helical path" is what "corkscrew" means when used as a verb, yes. It has nothing to do with corkscrews-the-noun aside from the shape.

@nick012000 My interpretation makes more sense to me.

The corkscrew motion of the propeller is what causes the lift that causes thrust.
A propeller is, effectively,  a tiny wing that pushes air backwards through the use of aerodynamic forces - that is, it generates lift. Like any wing, it generates this lift through its motion through the air, with the angle between the wing and the air body being referred to as the angle of attack, and the angle of attack plays a key role in the generation of lift.
In the case of the propeller, this angle of attack is created by the corkscrew motion of the propeller through the air: the propeller moves in a circular pattern around its base by its engine, and the plane as a whole moves forward through the air. If you were to break an instance of this motion into its components from the point of view of the propeller blade, you'd see that the rotation produces a motion "back" along the propeller blade, while the lateral motion of the plane produces a motion "down", and you'd add these together to calculate the relative wind velocity vector, which in turn would be used to calculate the angle of attack of the propeller blade along with the lift and drag forces it produces.
Like any wing, a propeller produces lift both by generating a low pressure region on top of the wing, and by redirecting air downwards through the laminar flow of air over its surface.

AoA is everything. With a blade pitch of zero, you don't go to space today.


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How far could a KC-10 tanker fly if it consumed all of its internal fuel tanks?
I have read that the KC-10 tanker aircraft carries a maximum load of 356,000 lbs of fuel. It also consumes the same fuel that it carries for refueling other aircraft. So naturally, I am wondering: If the KC-10 took off at max weight and flew continuously until forced to land, how long would it fly? How far would it have flown in that time?
I just want a ballpark figure but I don't know how to go about estimating one.

If you find the fuel burn per hour at cruise of the KC-10 you could determine a rough estimate.

Welcome to Av.SE!

For a transport airplane like this, it's roughly 1/3 structural weight, 1/3 payload, and 1/3 fuel. For a tanker the payload is also fuel, so the total range is roughly double of its airliner cousin.

Not too hard to work out an educated guesstimate.
The CF6-50 used in the KC-10 has a thrust specific fuel consumption of .375-ish lbs fuel/lb-thrust/hour.  Takeoff thrust is in the range of 53000 lbs.
Cruise thrust can be anywhere from 25-35% of max takeoff thrust depending on how fast you want to go.  Let's say 30%.
30% of 53000 = 15,900.  X .375 = 5,962 lbs/hr per engine.
Times 3 engines = 17,887 lbs/hr total fuel burn.
With 356000 lbs on board, it works out to 19.9, we'll say 20ish hours absolute endurance.  Deduct a little bit to account for takeoff and climb.
Say you're able to get it to around Mach .8, or 460 kt true at 35000 ft.  That gives an absolute range of somewhere around 9000 nautical miles.
Allowing for my sloppy quick math and different power settings, and takeoff/climb burn, a good ballpark range would be somewhere between 8-10,000 nautical miles and somewhere around 17-23 hours in the air.

Wikipedia claims a ferry range of 10,000 nautical miles, so there you go, math still works!

Cool!  I'll bet that's by slowing it down to M.7 or something.

Ugh, that's a long time in the air!

The Canadair Argus, a Bristol Britannia with R3350 turbo compound radials, optimized for maritime patrol, had a patrol endurance of 29 hrs at normal cruise, and low 30s dialed back from that.  The R3350TC had the specific fuel consumption of an automotive diesel.

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Is an airfoil's critical angle of attack measured using "geometric angle of attack" or "effective angle of attack?"
One of the first things we learn about stalls is that they occur when a wing exceeds a certain critical angle of attack, which depends on the specific design of the wing. But if a given wing has a critical AoA of, say, 20 degrees, which definition of AoA are we using?
As shown in the image below, geometric angle of attack is measured between the wing chord and the undisturbed relative airflow.
Effective angle of attack takes into account the induced downwash caused by wingtip vortices and is therefore smaller than geometric angle of attack.

These definitions of AoA come up in explaining induced drag, but I never see them referenced in discussions of critical AoA. I am assuming that critical AoA is measured using geometric AoA, but is this correct?
As a follow up question / comprehension check: Induced drag occurs because lift is produced perpendicular to relative wind. When the airflow is deflected downwards, the lift vector is in turn deflected rearwards, contributing to drag. Would it also be correct to say that the magnitude of the lift vector is decreased, since the effective AoA is shrunk, compared with geometric AoA?

In general, measuring something in respect to something which is inherently variable doesn't give a good measure: induced angle changes continuously according to the lift distribution and it is actually not even well definable at stall. Using it to represent the aerodynamic characteristics of a wing would just make the measurements difficult. The geometric chord line must therefore be used. Furthermore, induced angle is just a more or less correct (less than more) logical/mathematical construct to help understand and visualise induced drag, it is not exactly something real.
A wing stall is also different than a single airfoil stall: wings (at least the ones of a GA or jetliners) are made to be as much resistant to stall as possible. Wing twist, aspect ratio, spanwise chord distribution and other parameters are all chosen (also) to retard and give a stall as smooth as possible. Typically, the stall begins at the root of the wing so that its turbulent wake impinges on the tailplane making it vibrating and warning the pilot of the imminent stall.
The following plot (red squares) shows the lift coefficient of a Cessna 172 (source - I couldn't find the origin of this plot, but it comes up quite often searching it around and it looks plausible):

Maximum lift coefficient is some 1.6 at 16°. Now compare it with the plot for the NACA 2412 which is used as basis airfoil for its wing:

As you can see the maximum lift and the relevant AoA are the same as for the whole wing but look how much smoother the stall region is for the wing in comparison to the the airfoil.

The goal of starting a stall at the root rather than tip is to minimize roll effects and to retain aileron effectiveness as late as practicable. Having the stall advance along the wing rather than occurring over the full span softens the onset.

@MaxPower: yep, that as well. You can expand my answer if you will

When we talk about stall and other things, the angle of attack is the angle between some geometric reference line (the chord for an airfoil, some datum line for a whole aircraft) and the freestream velocity.  I.e. your 'geometric' angle of attack.
The stall AoA for a wing will not be the same as the stall AoA for an airfoil (even if the wing is constructed from that airfoil) because of 3D effects including downwash and the effective angle of attack.
Consequently, a 3D stall AoA for a wing essentially "builds in" the effect you're seeing.
Of course, most wings do not stall all at once.  Stall may start at the wing tips (or the root) and will progress as the angle of attack is increased.  Precisely defining when 'stall' happens for a wing can be complex -- is it when the first signs of stall are deteced?  is it when the lift coefficient attains its maximum value?

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Air density decreases as temperature increases - but air also gets cooler as it expands; does this create a feedback loop?
First, I apologize for the sloppy title. I had a tough time phrasing this as a concise question.
For a column of air at a given pressure, density decreases (the air expands) as temperature increases.
At the same time, however, adiabatic cooling seems to represent the opposite phenomenon. As a parcel of air rises, it expands due to a decrease in ambient pressure. This expansion results in fewer collisions between air molecules, thus its temperature decreases.
In other words, higher temperatures cause air to expand, but expansion causes air to cool. Does this result in a kind of feedback loop (i.e.: air expands, thus cools, thus contracts, thus warms, thus expands...), with temperature and density ultimately reaching a kind of equilibrium? Or are these two phenomena totally unrelated? Is there something else I'm misunderstanding altogether?
Thanks for any clarification and I hope this question makes sense!

I think this would be a better question for Physics.SE. I don't see any relation to aviation.

@Bianfable Hmm, that may be fair. The question occurred to me through studying aviation weather theory, so this is where I thought to ask it.

"density decreases (the air expands) as temperature increases" – yes, when you add energy while keeping pressure constant. That is how a hot air balloon works. If expansion is caused by reduced pressure, temperature decreases.

Under extreme conditions, such as a rocket exhaust, there may be something along the lines of your thinking in the form of the diamond pattern.  Not seen in weather as heating/cooling and volume changes are many orders of magnitude smaller.  See the SR-71 Blackbird jet exhaust.

@Bianfable, understanding the medium in which aircraft operate absolutely relates to aviation.  It is more relevant in my opinion than a lot of the database type questions we see here...

@MichaelHall Sure, we get a lot of questions about the atmosphere that are very important to aviation. But this one isn't! It is about basic physics (thermodynamic processes, ideal gas law) without any relation to aviation.

@Bianfable -- this is totally related to aviation, especially soaring.  Every glider pilot would be interested to know about it, if a chunk of atmosphere tended to start "boinging" up and down (insert appropriate noises from Wiley Coyote and Roadrunner cartoon here) due to the mechanism proposed in the original question.  Could make for an "interesting" flight--\

Appreciate the meta-engagement generated by this question. For what it's worth, I was asking the question totally from a place of curiosity and just trying to better understand weather theory, and not because I thought it would have any immediate practical benefit to my flying. But it did definitely strike me as an "aviation" question, which I was asking because I'm a student pilot.

@EthanB a look at an atmospheric temp profile would help.  What helps drive rising air is the surrounding air is progressively colder and thinner as you go up.  With or without cloud formation (which helps it keep rising), most thermals away from their heat source will radiate their higher temperature away and dissipate into the surrounding air.  Any oscillation in the downward temperature pattern, if measurable, may make an interesting study.

"density decreases (the air expands) as temperature increases" – yes, when you add energy while keeping pressure constant. That is how a hot air balloon or a thermal works. If expansion is caused by reduced pressure, temperature decreases.
What happens in the atmosphere is normally described as an isentropic process.

I think this is the relevant point I'm looking for. When energy is added and pressure remains constant, the temperature increases and the air expands. But because the pressure is constant in this case, there isn't a subsequent adiabatic decrease in temperature, so the infinite regress or feedback loop suggested in my original question does not occur. Correct me if I'm wrong or misunderstanding.

@EthanB Yes, that's it. It helps to ask yourself whether a process would need the addition or removal of energy and where this should come from.

There are 5 players in your question, found in:

the gas equation P = nR/V × T, and relative humidity

For your question:

Density decreases as temperature increases

we can see lower density (nR/V) and higher temperature T will yield the same pressure and a greater volume.

Higher temperature causes the air to expand

The air parcel is now lighter than the surrounding air and rises.

But expansion causes the air to cool

The "contraction" is only due to temperature decrease.  With no change in pressure, no energy is going into the system to drive heating through compression. (Remember rising air is constantly moving into lower pressure). The contraction will be a thinning of the rising air column, as seen with the "classic" mushroom or anvil cloud.  It is simply a reduction in volume as temperature drops, with pressure remaining equal to surrounding air.
All fine and good until:  relative humidity gets too high. Moist air cools with expansion at a lower rate than dry air, and the lighter water vapor also contributes to its bouyancy.
Now the air rises much faster and higher, potentially leading to a thunderstorm.

ultimately reaching a kind of equilibrium

So, yes, with weather the phenomena are related through pressure, and humidity plays a key role.  Dry air, heavier than surrounding air of equal pressure but higher humidity, can be heated by compression as it sinks.  These are the famous Chinook or Foehn winds.  As the dry air sinks, the surrounding air of higher pressure compresses it.  This is the opposite of adiabatic cooling.

Correct!  See edits.


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Are there planes designed for going supersonic in a dive only, not in leveled flight?
Are there any sub-/transsonic planes that are able to go supersonic in a dive without damage nor losing control but can't go above Mach 1 in horizontal flight? Some planes can go into leveled supersonic flight on afterburners only, but I mean planes that don't have any.

Does the space shuttle count?

Also, Felix Baumgartner is designed to go supersonic in a dive but not in horizontal flight, but he is a person, not an airplane.

@QuadmasterXLII, designed, or evolved?!  ;)

Just "able to", or designed intentionally?  (you use both terms, but they aren't as interchangeable as you might think)  There are plenty of planes that could survive going supersonic in a dive, (the EA6B I flew being one of them, limited to subsonic when carrying any external stores...) but "designed" implies a specific mission requirement.

@MichaelHall I'd go towards designed intentionally, but if a plane can survive going supersonic in a dive it's built so that it can survive it. ;-) B737s for instance cannot go supersonic without damage and/or loss of some control.

@QuadmasterXLII The Space Shuttle and the Buran went supersonic during ascent too, but they're a more complicated matter.

@Giovanni, good point.  I’m sure designers consider the probability of an excursion in their design.  B737 - unlikely; a subsonic tactical jet performing defensive combat maneuvers - more likely.

@MichaelHall The Mig-15 reportedly got supersonic in a dive but control was impaired when flying supersonic, since then the MiG-15 flies no faster than Mach 0.92.

The V-bomber Handley Page Victor was designed to be a supersonic bomber, however its top speed ended up around 1050 km/h. I have read stories about it reaching supersonic speeds in dives. Not specifically designed to go supersonic in dives, but it did happen.

@Noddle A service ceiling of 56,000 ft, it seems to have been among the highest-flying sub-/transsonic planes ever.

Maybe not designed but achieved

@Dave Yeah I knew the DC-8 story, but I rather mean military jets. SilkAir 185 went supersonic as well. https://en.wikipedia.org/wiki/SilkAir_Flight_185

@Giovanni One of my favorite planes! HP Victor looks so mean and futuristic in its design. The reason for its odd shape, both the fuselage and the wing, was to ensure that shock waves would appear at the same time on the entirety of the plane during transsonic flight.

Pretty much every early jet comes to mind.
Think the Me262, the F-86, the Mig-17. All could go slightly supersonic in a dive without damage (if not kept up for long, obviously) but not in level flight.
I've heard that some jetliners can go slightly supersonic in a dive without damage. Again, only if they pull out quickly and don't stay in the supersonic regime for more than a few seconds, but I've not seen hard data on that.
I've also heard of a souped up G650 that can go supersonic in a shallow dive and and maintain that once reached in level flight and is actually rated for it with a limit of 10 minutes between inspections (iow, the certification authorities are confident it will not take damage for the first 10 minutes of supersonic flight). But that might be exageration on the part of the person who told me about it (supposedly it's a one off conversion including uprated engines, an extra fuel tank, and stronger structural beams).
I'm sure there are other examples.

I didn't even know there's still a civilian airplane that can go supersonic (if your source is correct about the G650).

@Giovanni neither did I and though my source may have misunderstood some details they're not prone to bragging.

Given the fact that some airliners have gone supersonic during incidents and some recovered, it may well be possible. The G650 and 700 are transsonic already anyway.


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On the G1000 lean assist page, what does a positive delta EGT mean?
When leaning the fuel mixture on a C172 using the lean assist feature on the G1000, the hottest cylinder's EGT will be displayed, along with a reading showing the difference between the current temperature and the peak temperature recorded.
Whether rich or lean of peak, the delta should be negative, indicating a temperature colder than the peak. In practice, however, this number can be positive. What does this mean? Isn't a temperature "hotter than peak" simply a new peak temperature? Does it mean a different cylinder has surpassed the original cylinder's peak? (I am allowing the G1000 to automatically select the hottest / displayed cylinder.)
The instructions for leaning in the POH say to find peak, then enrich the mixture to 50 degrees below peak. How do I incorporate positive delta peak readings into this process?

I believe I have found the answer to my question in the G1000 manual (previously I had looked at the POH for the C172 NavIII).

The ASSIST Softkey aids in the leaning process by identifying the peak of the first cylinder whose temperature falls.  This cylinder’s number below the EGT bar graph is highlighted in light blue as the selected cylinder.  If the temperature of the peaked cylinder exceeds the peak value, the peak value is not updated.  Monitoring of the
cylinder continues until the ASSIST Softkey is pressed again which disables lean assist, and removes the peak block from the bar graph and the temperature deviation from peak (ΔPEAK)

(emphasis mine)
This suggests that as soon as one cylinder's temperature drops, the temperature it had reached right before dropping is considered the peak. Even if it should get hotter that that temperature as the mixture is further leaned, the original peak remains the point of reference for the ΔPEAK indicator.

This most likely is the correct answer, however, later version of G1000 handbooks have omitted the paragraph you cited, for whatever reason.

Thanks for chiming in @ymb1 I'll delete my answer. I'm pretty sure I've seen what it was based on somewhere, but since I cand find it anymore, well, might just be the early stages of dementia then


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Is a balloon's record altitude measured from the top of canopy, the bottom of the basket, or some other point?
I wonder where exactly on the balloon is its altitude measured. By the time a space balloon reaches its maximum altitude it is extremely large, the higher the larger. The record altitude for a balloon is 173,900 ft (53 km) by BU-60-1, but what part of the balloon did measure that value? The ceiling of the balloon? The bottom of it? The pod attached to it? If it was the pod, it would mean the balloon itself was higher.

Per the description of BU-60-1 at JAXA it carried a suspended payload with several cameras and a GPS receiver to measure altitude. While the top of the balloon would indeed have been higher, the FAI rules linked by mins in a comment indicate that record altitude claims are read at the instrument, suggesting that the claimed altitude would be that measured at the suspended payload in this case. Though it would appear you could try to gain another 100 meters or so by mounting it higher up. Physics would tend to make this tricky and would impact the credibility of any serious program to do so (JAXA seems to have been more interested in total lifting capacity rather than peak altitude).
In anycase if chasing a altitude record it would seem better to cut payload mass (delete cameras etc) rather than trying to mount a payload on top and then need a counterweight at the bottom that is dead weight.


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If a plane was put into a vacuum chamber, what would its altimeter read?
Just curious. What if you put a (general aviation or airliner) plane into a hard vacuum chamber? Would its altimeter simply read the highest possible altitude it could? That's rather impossible for general aviation planes as their altimeter can theoretically go on infinitely. Or would the altimeter simply fail?

"their altimeter can theoretically go on infinitely" [citation needed]

@Federico General aviation aircraft usually have analog pointers, not digital screens showing the altitude. You wouldn't know whether the pointer shows 1,000 ft or 101,000 ft as it would look the same for each 100,000 ft.

the fact that the arms seem to be able to rotate indefinitely, does not mean that they can, theoretically or practically.

@Federico Alright, but that's what I meant by "theoretically go on infinitely" and GdD's answer explains why it cannot do so practically.

Analog altimeters are mechanical devices which have a set of air filled discs called aneroid wafers inside which expand or contract with air pressure changes. The expansion or contraction of the wafers is translated to rotational movement which turns the pointers. As air pressure decreases the wafers will expand to their maximum, then stop as they can't move any farther, further decreases in pressure will not increase the altitude readout. A full vacuum may rupture the wafers, which would make the instrument inoperable.

Electronic instruments will behave as they are programmed, so the answers are likely to differ by manufacturer. Although I have no direct experience with this I would expect that when the sensor's pressure data gets below a certain threshold that the computer is more likely to show it as an error rather than show the airplane being at an altitude that's impossible. Ladies and gentlemen, we are not cruising at 150,000ft, I know that much!


text:
Flight directional headings
I listen to aircraft land and take off weekly.  I noticed in taking off they usually only use about 3 to 5 different directions.  I don't understand what they mean when for example they said to the pilot, "American 1450, ok for take off 27 left, head 265"  The only part I am concerned with, the part I don't understand is the heading part.  What does the 265 represent?  The next plane was told to line up and wait.  Shortly it was told that it was ok for take off, but to head 235.  Please explain.

What you are hearing is a departure clearance. ATC is giving instructions to pilots on the ground before they take off on what runway to use and what to do next.
27 Left is the runway, which points close to 270 degrees. We shorten it to 27 because although it may not be exactly 270 degrees that is close enough. 27 Left means there are more than one runway in parallel, if there's a 27 left then there's a 27 right.
The second part of the clearance is the departure heading. 265 is very close to the runway heading, so ATC is telling the pilot to maintain runway heading. The second flight ATC is telling to make a left turn to 235 after departure, this is either to get the flight closer to its destination heading, or more likely for spacing to keep the flights separated. There was probably an altitude instruction in there somewhere, like 'climb to 2000ft, then turn left to 235.'

Depending on the airport, 265º may in fact be runway heading for runway 27L.


text:
How should I log training time in an aircraft that requires two pilots, while I'm the sole manipulator of the controls?
Very specific and narrow question.
Part 91 operation, training and flying LR-45 - 2 pilots required. Not 135 regs, not 121 regs, not 91k regs, part 91 only (Class G space)
How would I log the training time while being the sole manipulator of the aircraft controls (acting as PIC or supervised PIC) during training for the SIC only rating?
The supervising pilot is ATP and CFII with all of the requisite type ratings.
I am a commercial pilot with AMEL and Instrument ratings and all required endorsements for the operation of the LR-45.

§ 61.51 Pilot logbooks.
(a) Training time and aeronautical experience. Each person must
document and record the following time in a manner acceptable to the
Administrator:

Training and aeronautical experience used to meet the requirements for a certificate, rating, or flight review of this part.

The aeronautical experience required for meeting the recent flight experience requirements of this part.

[...]
(e) Logging pilot-in-command flight time.

A sport, recreational, private, commercial, or airline transport pilot may log pilot in command flight time for flights-

(i) Except when logging flight time under § 61.159(c) [SIC TIME, when the pilot
is the sole manipulator of the controls of an aircraft for which the
pilot is rated, or has sport pilot privileges for that category and
class of aircraft, if the aircraft class rating is appropriate; [CLASS MULTI ENGINE LAND]
(ii) When the pilot is the sole occupant in the aircraft;
(iii) When the pilot, except for a holder of a sport or recreational
pilot certificate, acts as pilot in command of an aircraft for which
more than one pilot is required under the type certification of the
aircraft or the regulations under which the flight is conducted; or
(iv) When the pilot performs the duties of pilot in command while
under the supervision of a qualified pilot in command provided -
(A) The pilot performing the duties of pilot in command holds a
commercial or airline transport pilot certificate and aircraft rating
that is appropriate to the category [AIRPLANE] and class of aircraft being flown [MULTI ENGINE],
if a class rating is appropriate;

There is no mention of the requirement of having a type rating in order to log the PIC time or SIC time, obviously without a type rating the pilot being trained cannot be the "Pilot In Command" of record but the regs seem to indicate that PIC or SIC time may be logged by a pilot
"when the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated, if the aircraft class rating is appropriate;" emphasis no mention of Type rating required to LOG the time. I understand the not being the PIC of record - just the log is what I am clarifying - and no I am not worried about what the airlines or the next employer is going to ask about the time, so let's not go there.
As far as the FAA is concerned for the ATP time requirements what would be the correct manner of noting the time spent acting as the sole manipulator of the controls of an aircraft that requires by certification two pilots for its operation, assuming I have met all of the other requirements other than the type rating?
Lets see if I can get one logical and correct answer based upon the regulations and not feeling and beliefs. If it's not in the regs, ignore it.
And I would agree with your answer about the requirements for a type rating and your well reasoned response except for one small word later in the regulation.
At the end of
(III) there is an or

(iii) [...]; or
(iv) When the pilot performs the duties of pilot in command while
under the supervision of a qualified pilot in command provided -
(A) The pilot performing the duties of pilot in command holds a
commercial or airline transport pilot certificate and aircraft rating
that is appropriate to the category and class of aircraft being flown,
if a class rating is appropriate;
(B) The pilot performing the duties of pilot in command is undergoing
an approved pilot in command training program that includes ground and
flight training on the following areas of operation -

Preflight preparation;

Preflight procedures;

Takeoff and departure;

In-flight maneuvers;

Instrument procedures;

Landings and approaches to landings;

Normal and abnormal procedures;

Emergency procedures; and

Postflight procedures;

(C) The supervising pilot in command holds -

A commercial pilot certificate and flight instructor certificate, and aircraft rating that is appropriate to the category, class, and
type of aircraft being flown, if a class or type rating is required;
or

An airline transport pilot certificate and aircraft rating that is appropriate to the category, class, and type of aircraft being flown,
if a class or type rating is required; and

(D) The supervising pilot in command logs the pilot in command
training in the pilot's logbook, certifies the pilot in command
training in the pilot's logbook and attests to that certification with
his or her signature, and flight instructor certificate number.

"Or"
negated everything listed prior to the "or"
All of the items listed after the word "or" are applicable in this situation so I am trying to figure out what I missed.
Thank you for your consideration.

Welcome to aviation.SE! I reformatted your question a little to hopefully make it clearer. If I changed it too much then you can simply edit further yourself or roll back my changes. Could you clarify what it means when you say you have "all required endorsements for the operation of the LR-45"?

The issue for you is (iii)(B).  Are you going through an approved pilot in command training program.  If so, that would require FAA approval and a LOA issued.  Can your ATP and CFII rated pilot provide such a document?  Those are usually reserved for Part 135 operations

That is the correct jeopardy question. Ding ding ding. For anyone out there get the LOA for the PDP prior to the training. Otherwise you will be sad as you remove all of the PIC time from your logbook. :-(  don't make the same mistake that I did. Thank you for the answer that resulted in a bad outcome. Better than presenting the hours for the ATP certification and getting a really bad outcome.

There is no mention of the requirement of having a type rating in order to log the PIC time or SIC time.

This is not true.  The regulation you mentioned clearly says this:

when the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated

The word rated includes type ratings such as the Learjet 45. See 61.5(b)(7) for a listing of ratings you can place on your pilot certificate.  Since you are not rated, you cannot log any PIC time in that airplane.
As for logging SIC time.  Refer to §61.55.  You need to have:

(b) Except as provided in paragraph (e) of this section, no person may serve as a second-in-command of an aircraft type certificated for more than one required pilot flight crewmember or in operations requiring a second-in-command unless that person has within the previous 12 calendar months:

(1) Become familiar with the following information for the specific type aircraft for which second-in-command privileges are requested -

(i) Operational procedures applicable to the powerplant, equipment, and systems.
(ii) Performance specifications and limitations.
(iii) Normal, abnormal, and emergency operating procedures.
(iv) Flight manual.
(v) Placards and markings.

(2) Except as provided in paragraph (g) of this section, performed and logged pilot time in the type of aircraft or in a flight simulator that represents the type of aircraft for which second-in-command privileges are requested, which includes -

(i) Three takeoffs and three landings to a full stop as the sole manipulator of the flight controls;
(ii) Engine-out procedures and maneuvering with an engine out while executing the duties of pilot in command; and
(iii) Crew resource management training.

Once you have been trained by any type rated pilot and they have endorsed your logbook [61.55(d)(1)], you can then act as a second in command on flights carrying passengers. [See 61.55(f)(3)]

As far as the FAA is concerned for the ATP time requirements what would be the correct manner of noting the time spent acting as the sole manipulator of the controls of an aircraft that requires by certification two pilots for its operation, assuming I have met all of the other requirements other than the type rating?

Only log the time you are acting as the second in command which should be the total flight time.  You cannot log PIC time as you are not rated in the airplane.
As far as meeting the aeronautical experience for an ATP certificate.  You will need 1500 hrs of pilot time which includes PIC and SIC time.  There are only a few requirements that must be met as PIC (sole manipulator of the controls, etc...)
Examiners know these rules and every FAA inspector with the task of oversight of DPE and other examiners ensure these rules are followed.  It is quite easy for examiners to ask non-threatening questions to see how the flights were conducted and then decide to not accept those times for the certificate or rating sought.


text:
What if you have a double-engine failure after V1 but before VR?
Imagine an A320 on the runway, starting its take off roll. The PM calls out "$V_1$". Just a second after $V_1$ is called out, and before $V_R$, you encounter a double-engine failure (an A320 has only 2 engines). Now, you've got no engines working. You also have less than the runway length required for you to decelerate on the runway. What should you do next?

Get on the brakes and hope what's beyond the runway is soft.

Kudos for the longer answers, but Ron here has pretty much the core actions covered.

I mean, the decision is made, right? The plane will not fly so it must be stopped. The pilots should do whatever possible to slow the airplane as much as possible before sliding off the end of the runway.  Energy is not your friend in this case.

Isn't the question rhetorical? If all engines failed, takeoff definitely isn't an option, so the other remaining option is break. Or do you think of alternatives? "Tertium non datur" (There isn't a third way) I'd say.

@U.Windl, Brake to reduce break.

OK, non-native mixed up break and brake, sorry. "De-accelerate rapidly" I wanted to say.

Bend over, put your head between your legs, and kiss your butt goodbye.

The Airbus A320 FCTM (Flight Crew Training Manual) does not describe any procedure for rejecting a takeoff after reaching V1:

The decision to reject the takeoff is the responsibility of the Captain and must be made prior to V1 speed

Nothing further is mentioned about rejecting at a later time. However, the FCTM and also the QRH (Quick Reference Handbook) never even consider a dual engine failure during takeoff. Only a dual engine flameout at high altitude is considered. Not even a dual engine failure at low altitudes is mentioned, although my copy of the FCTM is a bit older, so it does not include the changes made after AWE1549 (the miracle on the Hudson). The final accident report says

US Airways’ dual-engine failure training, which was provided during initial training in a
full-flight simulator session, was consistent with the training provided by Airbus. The
dual-engine failure scenario was presented at 25,000 feet, included two engine restart attempts,
and was considered complete after the restart of one engine [...]
No
dual-engine failure training scenarios were presented at or near traffic pattern altitudes [...]

I assume they made some changes after this accident.

The Boeing 737 NG FCTM actually mentions rejecting above V1:

Rejecting the takeoff after V1 is not recommended unless the captain judges the
airplane incapable of flight. Even if excess runway remains after V1, there is no
assurance that the brakes have the capacity to stop the airplane before the end of
the runway.

Rejecting after V1 is only allowed if the airplane is incapable of flight. This is certainly true after a dual engine failure before VR because you cannot climb safely below V2 (and you cannot maintain V2 anyway). Even the attempt to rotate the plane before VR would likely result in a tailstrike.
The Boeing 737 NG FCTM further shows the effect of a late reject decision:

As you can see in this example case, where the rejected takeoff (RTO) was started 2 seconds after V1, the airplane would be moving at 75 kt at the point where it would have come to a complete stop if RTO had started at V1. The airplane then comes to a complete stop 210 m later.
However, this does not necessarily imply that the airplane leaves the runway. That is only the case if V1 is limited by runway length. If V1 is instead limited by Vmbe (maximum brake energy), there would be more runway available, but the brakes might fail before coming to a complete stop. The best case is if V1 is limited by VR, which might give you both enough runway and enough stopping power to come to a complete stop (your scenario describes the failure between V1 and VR, so this cannot be).
In any case, the best decision if the airplane is incapable of flight is to attempt an RTO. It is better to crash at low speed than to crash at high speed after trying to get airborne. The runway might even be equipped with an RSA or EMAS, which reduces the risk of severe damage and helps to stop sooner.

"It is better to crash at low speed than to crash at high speed" Not to mention better to crash at ground level than fall even a few tens of feet from wherever you stall after a no-power rotation.

One-engine failure (OEI) and all-engines failure are not approached the same way.

Today an engine failure during takeoff is an event with a very small likelihood. Engines are tested and proved to be resilient, bird strikes and FOD ingestion are made infrequent by prevention. Still this can happen.

On the other hand, a double engine failure during takeoff has a likelihood which is insignificant.

The different likelihood associated with these two cases are not mitigated the same way:

The event with the highest likelihood, the single engine failure, is reduced by the takeoff protocol involving V1 speed and allowing the crew either to stop safely before V1 or to takeoff safely after V1. The price to pay for this safety is it requires a longer runway. This constraint has been accepted by airlines and airport managers.

The double engine failure preventing to take off, has no economically viable solution. It was decided runways all over the world wouldn't be extended to allow a normal and safe stop at a speed higher than V1. So the aircraft must be stopped using all braking means available. And if this is not possible, the aircraft will leave the runway. Airports are designed to not make this accident worse than it is, e.g. obstacles like lights, signs or poles are required to be frangible at ground level..
However some last resort feature can be put in place at the end of the runway to stop the aircraft with exceptional means. This can be a safety net for military, or an EMAS for civil aircraft:

EMAS, source

EMAS are useful both for takeoff and landing, to prevent runway excursions. So they tend to be more acceptable economically. There are several questions on the site about EMAS. However EMAS and similar arresting system are not full guaranties for a safe stop, the aircraft has still to roll in straight line to reach them.
For events that are assessed and found to be very unlikely, there is no specific solution except prevention, crew best judgment and skills to manage the unexpected. This is not different from other domains.
What would the crew do? They would brake using all possible means and use their skills either to maintain the aircraft on the runway, or on a taxiway, or anything they can do.
@Bianfable has detailed some of the guidance available in his answer.
In this scenario, many elements have been anticipated, random examples:

Thrust reversers would be inoperative, but aircraft demonstration for certification requires to brake without reversers.

Brakes would likely be excessively solicited and possibly a fire can start. Aircraft certification requires this fire to be contained to the wheel for 5 minutes, the time for firefighters to access a crashed aircraft

The tires mustn't explode but deflate.

If you have reached 88 miles per hour, immediately activate the flux capacitor and quickly select a year.
If both engines have failed there is no choice to make. You aren't going flying.  Abort immediately and you will eventually stop... somewhere.  Brake at maximum capability, ensure spoilers deployed automatically when you pulled the power to idle.
The thrust reversers won't have any thrust to reverse. It could be argued/debated that deploying them could create some minimal drag/cancel any residual thrust while the engines spool down.

What else can you do? Follow your rejected takeoff procedures and hope like hell you can stop in the runway remaining.

Again I suppose it’s all tied to how much runway you have left. It’s possible you have quite a bit of runway beyond what was required for a balanced field length calculation.  If however very little runway remains and a crash seems eminent or the plane is headed for an EMAS patch hat the end of the runway, yeah I think the captain would immediately issue the “brace for impact” command.

Do not attempt to fly a plane incapable of flight!
What goes up must come down.  The "coming down" will be Very Bad, and occur probably at destructive vertical speeds and definitely at a site not engineered for that purpose.
As my martial arts teacher says about falling... you are already on the ground.  So is a rolling airplane.  While you may not be able to stop in runway length, your collision energy will be much lower by the time you exhaust the remaining runway, because you have used that remaining runway for max braking.
And most runways have been engineered for runaway overruns, with crushable things like "breakaway" lights and antennas (a great deal of experience crossed over from highway design) inside the fence... and easements outside the fence so that hard things are not built along the extended runway center line.


text:
Why don't most planes fly in a straight path?
Take a look at these images:

As you can see, in all the images, the flight paths are curved. As far as I know, the shortest path between two points is a straight line. Planes usually would take the shortest path so that they can save fuel, money and time. Then why are the flight paths curved? Why don't planes fly straight to their destination?

See also Can longer paths consume less fuel than the (shorter) great circle path? and Why was Pan Am Flight 103 flying over Lockerbie?

Because the straight path between two points on a globe leads through the globe.

Regardless of the optimal "most direct" route, planes also fly not-directly because there are other airplanes in the sky. ATC will route aircraft in ways that are most efficient for most users while preserving some sense of regularity and order that allows for safety. For example, see this question about arrival and departure gates at busier airports.

It's because the massive nation of Greenland.  All that landmass (larger than Africa) houses a secret technological society, which secretly controls the world.  By their edicts, all airplanes must fly curved routes.

If only the Earth was flat.

And this - my friend - is the day you learn about xkcd: https://xkcd.com/977/ I hope you haven't any work planned for today.

Because the earth is made of hard stuff that would slow the plane down too much.

In short
This is counterintuitive. Ignoring Earth curvature not shown on maps, the routes which appear curved on the screenshots are actually nearly straight. Compare these two different projections:

This is the same track, the same geographic landmarks are crossed. Still:

Left: We sense a bulging disk, the path is nearly parallel to two opposite meridians forming a circle, it must be a straight path.

Right: The path doesn't seem parallel to any meridian and we can't make sense of the heading change over Greenland. Difficult to see a straight path here.

Websites don't use the azimuthal projection of the left side because the map must be drawn with the path close to the center, while Mercator projection is unique for the whole Earth. But there is a growing demand for an adaptive map representation, adjusting the projection while zooming in/out. With current server and client processing capabilities this is possible, see this demonstration.
Commercial routes are as straight as possible, deviations are due to constraints, e.g. the maximum distance to available emergency airports, weather/conflict unsafe areas and unfavorable winds.
Details follow.

Mercator maps
In 3D, a "straight path" on a sphere is a curve. Our brain is able to identify such curve "as straight" on azimuthal projections, but on other types of map projection, specially on Mercator maps, such equivalence makes no sense. Example with azimuthal projection on the left and web Mercator on the right:

The shadow represents the night, and of course the separation between night and day is a circle, a straight path for an aircraft. It's not difficult to accept the idea the path is straight the left, but on the right, it's nearly impossible. However looking closer, we see the path crosses the same landmarks.
The map on the right side is representative of maps used on websites, a Mercator projection using a cylinder tangent to the equator:

Mercator projection, source: Encyclopedia Britannica
The only places the map is accurate is along the equator. At any other latitude, it is distorted, the distortion increasing as we get closer to the poles. It's nonsense near the poles where the meridians never converge, giving Greenland (2 million km²) the size of Africa (30 million km²).
On the image above, features are projected along straight lines. Latitude $\small \phi$ corresponds to map vertical coordinate $\small y(\phi)=r \tan \phi$. Mercator projection actually uses Mercator function, equivalent to $\small y(\phi)=r \ln(\tan(\pi/4+\phi/2))$, in order to make it conformal, the goal Mercator was actually seeking after to make ship navigation easier. The aberrant polar regions are never shown.
Your maps: Los Angeles to Grozny and Dubai
Below is a portion of the great circle from Los Angeles to Grozny, which is approximately the route shown on your last screenshot:

On the right, the Mercator map shows it curved. Parallels and meridians are circles, note how they have been converted into straight lines. This conversion introduces large distortions:

Greenland looks the same size as Africa, see the True Size of Countries to understand how much this is wrong.

All great circles except for the equator and meridians are curved, more strongly at higher latitudes.

The heading is actually constant, but near the pole, the straight line (great circle) seems to make a U-turn. This is the most counterintuitive aspect.

The flat distance for LA-Grozny on the web Mercator projection (EPSG:3857) is 18,300 km, but the real ellipsoidal distance (on WGS 84 ellipsoid) is only about 11,300 km.

This is too much to compensate for, we're not trained for than.
The flight on your last screenshot (UAE37V) was ultimately heading to Dubai. The shortest path would have put it further North than the path it actually used. This is the great circle from LA to Dubai:

Great circle from LA to Dubai, the shortest route for UAE37V
The projection problem is manifest: the aircraft is following the 120°W meridian then the 60°E meridian. These meridians are (180°) opposite on the globe and form a continuous circle. However, on the Mercator map, this circle is folded at the pole and the two meridians are made parallel lines. So the aircraft seems to turn near the pole, while it actually continues flying straight ahead.

A Mercator projection is not simply 'a projection on a cylinder tangent at equator', because it requires further mathematical elaboration. A simple cylindrical projection tangent to the equator is not conformal, as the Mercator is.  https://math.stackexchange.com/questions/42838/mercator-versus-cylindrical-projections

@xxavier, for someone just trying grasp the concept of a great circle the question you linked to is frankly a bit much.  Because the earth isn't a perfect sphere either.

@MichaelHall It's close enough to a perfect sphere that you need a very specialist situation for the difference to matter. The difference is about a third of a percent. Coincidentally that's exactly the size of a dimple on a basketball relative to the size of the ball.

@Graham, is the difference of a similar magnitude to the Mercator projection not being a "cylindrical projection tangent to the equator"?  Because that was my point...

The difference between a Mercator projection and a central cylindrical projection is very important. Pls compare this https://en.wikipedia.org/wiki/Central_cylindrical_projection and this https://en.wikipedia.org/wiki/Mercator_projection

To illustrate the difference with an example, a point on the unit sphere having a latitude of 0,7 rad (40,1º) will be mapped, in a central cylindrical projection, at a vertical distance of 0,84 units from the equator, while in a Mercator projection that distance will be of 0,77 units... It's quite significant... And for higher latitudes, it's much more...

@MichaelHall The distortion from both of those projections is several orders of magnitude worse than the error from assuming the Earth is a perfect sphere. (Unless you're only going around the equator, of course.)

@xxavier: You are right, $y$ Cartesian coordinate for Mercator is not $\small y(\phi) = R \tan \phi$, but Mercator's function, $\small \int \sec \phi ; d \phi$, to make it conformal, as his goal was to sell maps where loxodromes were straight lines. He painfully calculated the integral, another remarkable achievement, as the integral was formalized by Newton and Leibniz only later on. Mercator's function would be simplified as $\small y(\phi) = \ln (\tan (\pi / 4 + \phi / 2))$ after Neper discovered algorithms.

That is a straight path. It is the map projection being used that is curved.
This is because Earth is a round planet, not a flat surface, and creating accurate maps have always been a problem.
Take a globe and stretch a string between those two points and you will see that it follows the same path as the “curved” lines you have shown.

BREAKING: NORTH AMERICA DEVASTATED BY GIANT STRING, ORIGIN UNKNOWN

I am reminded once of a commercial flight where a passenger nearby mentioned to another passenger about being high up enough that they could see the different colors between the states at their borders. Sheesh!!!!!

As you know, Earth is not flat, but is rather close to a sphere.
So "the shortest path between two points is a straight line" does not actually work. The straight line between those two points would go through the Earth, which is quite challenging for most aircraft (!).
The shortest path between two points on a sphere is called the "great circle route". It's the intersection of a plane going through the centre of the sphere and the two points with the surface of the sphere.
Now, mapping a sphere to a flat surface is quite a challenge. Take a soccer ball, cut it in half, and try to lay it fully flat. Good luck. Or try to wrap a basketball with a sheet of paper without any wrinkles or tears. Not going to happen.
There are many different ways of doing that (called projections), which all have different properties, usually trying to conserve either distances or areas or angles, but never all of them at the same time (even though lots of people have tried and some maps are really funky. Just think about the poles: meridians on a sphere all converge to a single point (the pole), while meridians on many maps (and definitely on those you are used to, which use the Mercator or Web Mercator projections like the ones in your exemples) are parallel.
This distorts the representation of the route on the map.
Here's an example, generated with the Great circle mapper.
Your first route is roughly LAX to KEF. If you use an orthographic projection it does look like a straight line:

The exact same route, drawn using a rectangular projection, does look curved:

If you look at the points it goes through (e.g. intersections with state or US/CA boundaries or coastlines), you'll see that it's the exact same route, just viewed differently. You'll also see that it's quite close to the route on FR24. The remaining differences may come from:

Trying to take advantage of the jet stream (a high-altitude wind which flows west-to-east around those latitudes, which changes a bit all the time, and which can save a lot of time and fuel if you manage to get "pushed" by it as much as possible), or, the other way around, trying to avoid it.
Following navigation routes: like you follow roads to go from one place to another, aircraft follow pre-established routes from one waypoint to the next).
Avoiding other aircraft (this is actually one of the main goals of the navigation routes above).
Avoiding bad weather.
In some cases, especially transoceanic routes, making sure the aircraft is never too far from a diversion airport, though nowadays even a twin-engine aircraft can fly quite far from one, see ETOPS.
For some routes, avoiding the airpace of some countries, due to local conflicts (aircraft usually don't like flying over war zones which have a risk of stray missiles), or other geopolitical reasons.

A few more examples of routes which are straight but don't like they are:

JFK-SYD:

Note how it looks like it curves one way then the other. The inflexion point is over the equator.

KEF-SYD:

Yes, it is straight, going over the pole:


text:
If i own my own airstrip and have a friend from another country that owns a private jet, can they enter the country and land on my airstrip?
So i'm just curious as to what would happen if i owned a private airstrip on my own land and wanted a friend from another country to come visit. Could he just simply fly to me without a visa or anything? Or would it have to go through customs? And what would happen to someone that just flew onto my airstrip without telling anyone? Would anyone even notice?

The US Government has at least one entire agency that looks for stuff like this: the DEA.  They get help from the Coast Guard, for boats and "submarines", and the Air Force for aircraft.

They would need to first file a flight plan to cross the ADIZ or else they will get intercepted before making it to your field. Once they have filed the appropriate flight plane they can then only land at an airport of entry. You also need to supply your APIS manifest.

All civil, private aircraft entering the U.S. must first land at an
airport of entry before continuing to their destinations, unless other
arrangements are made with U.S. CBP. Advance notification must be
provided electronically to CBP by means of the eAPIS. See the APIS
section for more information.

In other words an airport that has customs. You can however make other arrangements with CBP as noted unless other arrangements are made with U.S. CBP. So you might be able to land at your private field but you will need to arrange that with CBP prior to the flight.
AOPA has a nice primer on crossing borders here.

And what would happen to someone that just flew onto my airstrip without telling anyone? Would anyone even notice?

Yes, they would notice...

Also they notice and act on this sort of thing: https://www.cnn.com/2020/07/13/us/meth-bust-ultralight-aircraft-trnd/index.html

I’m pretty sure the “other arrangements” means a Customs User Fee airport; they’re not going to come meet you in some random farmer’s field.


text:
Did commercial air planes in 1972 really not have some sort of automatic distress call equipment?
I've recently watched the 1993 movie Alive, "based on" the real events of Uruguayan Air Force Flight 571. I don't know how accurate it was, but the basic idea is that the pilots did a mistake and started going down with the plane, so that its tail hit a mountain top and the entire back part of the plane was cut off and people got sucked out mid-air. Then both the wings were cut off and the remaining part of the plane crashed into the snow with mountains all around in/near Peru.
GPS was apparently started in 1978. So I get that it didn't have GPS-based signals.
However, did they really not have some sort of automatic tracking signal used to know where the plane is at all times? Even if all electronics were destroyed in the crash, would it not have sent several signals back to the airports (or whatever is/was tracking air planes) so that they would know almost exactly where the crash occurred?
In one scene, they find a little pocket radio and are able to hear on it that the rescue mission/search party has been "called off"; that they have given up looking for them. I found this very strange. Surely they would not just "give up" like that before finding them, even if they are presumed dead? If only to retrieve the "black box" and learning more about what happened?
And, again, why did they call it off in the first place since they must have received signals about its near-final location? Were air craft in 1972 really so primitive that they relied entirely on humans to communicate with their voices over the radio their current position regularly? That sounds more like something that would be done in the 1920s or something. The more I learn about aircrafts in WW2, they seemed to have all kinds of mind-boggingly advanced and automatic equipment even then. But this took place in 1972!

Such technology doesn't even exist today. See MH370.

Short answer
In 1972, there was no automatic position reporting, this had to be done by voice when the aircraft was not in radar contact. Distress transmitters, which range can reach 150 km in favorable circumstances, were already used by military at some places, and were being generalized to commercial aircraft. However distress signals were not monitored by satellites like they are today, but from ground stations (including by ham radio-operators who since a long time play a significant role in disaster communications and localization), from airborne aircraft and from ships.
If the search team couldn't find the aircraft, it can be because no distress beacon was on the aircraft, because they searched at the wrong place, or because for some reason it was not active. Beacons of that era could fail simply because their antenna was destroyed, or shielded by metal debris. Automatic beacons could also fail to activate, and the team may be unable to trigger it manually because they cannot recover it.
You mention GPS, be aware GPS is of no help in position reporting. Like other positioning systems, GPS can be used by the crew to determine their position. They still have to report it to ground control by some means.

Details
Position determination vs. reporting
It is important not to not mix two different things: Position determination and position reporting. Today you may read everything is "GPS tracked", but this is inaccurate and misleading. While many systems track us in real time, like the cellular phone operators, this is not the case of GPS, because a GPS receiver is a just a receiver, it doesn't send any information nor interact with satellites.
In the case of aircraft, ground control using a radar is able to determine the aircraft location and can share it with the crew. Radars have a limited range, don't work well in mountainous area, and are not implemented in oceans. When no radar can be used, the aircraft crew themselves determine the position. Then this position must be reported to ground control to make them aware.
Position determination and reporting by aircraft

Position determination. Today includes GNSS (GPS, Galileo, Glonass, etc). At the time this happened GNSS didn't exist, but other techniques were used, most still used today: Inertial system, Loran, VOR, TACAN, etc.

Position reporting. At the time, when out of radar coverage, reporting was done by the crew by voice communication, at predetermined reporting points along the route. The need to report the position is part of regulation, e.g. for FAA in FAR 71.5:

§ 71.5 Reporting points. The reporting points listed in subpart H of FAA Order JO 7400.11F (incorporated by reference, see § 71.1) consist of geographic locations at which the position of an aircraft must be reported in accordance with part 91 of this chapter.

Today there are multiple techniques to automatically report the position, like CPDLC, the most used is ADS-B. ADS-B is coupled with a GNSS receiver. The GPS position is broadcast blindly by the ADS-B transmitter and can be received both by control for tracking and by other aircraft for collision avoidance.

Current integration of SSR (radar) and ADS-B/TIS-B, source

As ADS-B is not encrypted, actually anyone can receive the aircraft position, and this is what ADS-B tracking sites use first.
There must be ADS-B ground stations closer than radio horizon. So ADS-B suffers the same range limit than radar. But this is going to evolve quickly, in the next 3 to 5 years ADS-B will be received by satellites, and satellites will relay the reportings to ground control. See details below.
When the aircraft position cannot be tracked continuously from the ground, another possibility can be used when a crash occurs: A distress radio signal can be transmitted on a special frequency.
Distress transmitters
The distress transmitters have generally an automatic switch detecting the large deceleration associated with a crash. This radio signal doesn't need to transmit the position which can be determined by several techniques, from triangulation on the ground to Doppler evaluation from satellites.
Distress transmitters are known under different appellations, the one used by aviation is emergency locator transmitter or ELT.
ELT
At the time this accident happened, ELT were used by US military aircraft, perhaps not by Uruguayan military aircraft. In the early 70s the system was also required on commercial aircraft.
At this time ELT transmitted on the distress frequency of 121.5 MHz could be received by stations closer than the radio horizon. That could be ground stations or airborne aircraft, mainly those crossing the oceans. In non populated areas, a beacon triggered within a radius of say 150 km from a flying aircraft could still be detected and the information relayed to search and rescue organizations.

121.5/243 MHz ELT, source
To locate the ELT, search teams used triangulation techniques similar to direction finders used both by ground control and aircraft.
ELT have evolved to a detection from satellites which permanently monitor distress signals at any place. Triangulation techniques have been replaced by Doppler sensing based on the satellite velocity relatively to the searched beacon.
Such ELT transmit an identifier at time intervals on 406 MHz, a frequency constantly monitored by Cospas-Sarsat, a system made of two constellations of satellites, one in geostationary orbit at high altitude, and one at low altitude but constantly moving.
Most 406 MHz ELT are coupled with a GPS receiver to autonomously determine their position. The GPS-based position is transmitted on the 406 MHz signal, double-checked by Doppler sensing, and reported to the search and rescue organization.

ELT using GPS and Cospas-Sarsat, source
They still send a continuous signal on the old 121.5 MHz frequency in order to allow the ground search team to use short-range direction finders to reach the ELT.
ELT limitation
While ELT may replace continuous tracking for the purpose of search and rescue, this is still unsatisfactory, as both MH370 and AF447 accidents have shown:

In some crashes, ELT were not triggered.
ELT cannot work underwater
ELT may be destroyed in the crash or their signal shielded by debris.

There are some ELT which can be released before ground contact, especially on helicopters. However technology allows for better solutions, but this assume a significant change in existing air traffic control organization, switching from ground-based control to space-based control.
ATC switching to space-based ATC
Current aviation traffic control relies mostly on ground stations. When the aircraft flies over oceans the communication is broken (or at least unreliable).
To solve this problem with modern technologies, plans are being implemented, both in Europe and North America, to use satellites to track aircraft and these plans include a generalized use of ADS-B transmission by aircraft.

Thales / Aireon solution for space ATC, source
In anticipation of this deployment some operators are already using satellites to communicate their position at regular interval. They don't sent it to ATC since ATC is not ready to process it, but to their own operation control center. This was a lesson learnt from MH370.
MH370 had all the technology required to determine and report its position:

GPS and inertial navigation system for position determination.
ACARS to report its position.
a satcom link to transmit over water areas (the satcom transmitter position was determined by Doppler sensing, this led to searching water areas).

However the ACARS was configured to transmit only to ACARS land stations using VHF links, and was prevented to use the satcom link, for economical reasons as the flight was supposed to happen mostly over land.

There are still plenty of 121.5 ELTs around, having helped find several going off over the last few years through CAP. You just can't buy new ones on 121.5 anymore, but the old ones are still supported.

@JonCuster: 121.5 MHz ELTs still exist and 121.5 is still an international distress frequency, but 121.5 is no more monitored by Corpas-Sarsat. Current 406 MHz ELTs generally have also a 121.5 transmitter which is used as a homing beacon by the ground rescue team.

I agree that Corpas-Sarsat stopped monitoring 121.5, however there are plenty of non-satellites listening for it - it just may take a bit (or a lot) longer to be noticed depending on where it is going off. The ones in hangers at the airport tend to be noticed fairly quickly...

Again, I fully understand the 406 system and how it is better than 121.5, but 121.5 is still out there and will be for a long long time. In addition, 406 was not used in 1972, the timeframe of the OP's question, and it is quite likely that 121.5 was not being used much outside of the US.

There was an incident maybe 5 years back when a scrapped airplane still had it's elt in it. Some kids got inside (iirc) and tripped the transmitter. Quite a whoohaa in SAR when they were trying to find out who had crashed and where...

@Jpe61: I can't remember who she was, but maybe 20 years ago a solo round-the-world sailor triggered her Argos beacon at her hotel prior to her departure. At this time Argos was also used for distress. Same mess.

@Jpe61 - we get about a half dozen such incidents a year where I live - mechanic bumps it while servicing the aircraft, somebody tosses a spare one on the workbench and goes home, all kinds of things. Usually military or private, haven't seen a commercial carrier one in the last few years.

The Navstar program that we know as GPS today did in fact get its start in 1978 but was not considered fully operational for a decade or so later.  Even then the small receivers that we know today didn't come out until the 1990s.  The civilian use of GPS with the accuracy improved by removal of "selective availability" for aircraft navigation didn't exist until the year 2000 or so.  The need for more accurate navigation by civil aviation was made clear by a few international incidents of aircraft drifting into places they should not have been.  Before that GPS was considered a purely military asset by the US government, though non-military applications were not barred as far as I know.  Before GPS there were a number of satellite and land based radio navigation systems with varying degrees of availability and accuracy.  Over the horizon LORAN navigation would have accuracy of several miles and line-of-sight VOR would be accurate to several hundred feet.  These land based radio navigation systems should be able to keep people from flying into mountains.  Satellite navigation systems used and maintained by the US Army and Navy were for military use, and not all that accurate.  It turns out that close counts with horseshoes, hand grenades, and nuclear ordnance.
There were systems for automated sending of distress signals for a long time before 1972.  On ships of the era they might still see use of the old Morse code telegraph systems that would send a distress signal by use of a kind of clockwork mechanism to send the dits and dahs.  These could exist on aircraft too, though with some electronics instead of clockwork.
Around this time there was work on replacing the old distress systems that were based on decades old analog and shortwave radio with systems that had more automation and use of satellites.  They really didn't get any traction until the 1990s and are still hanging on in some places of the world.  GMDSS is the standard now but even in the 1980s you'd see communications equipment much like that used in World War 2.  Radios cost a lot of money and if it ain't broke it's hard to get people to fix it.  Also, getting a fancy new radio locator beacon won't do much good unless the people looking know you have it and have the hardware to look for it.  It's a classic chicken or egg problem.
The US military worked on radio location and navigation considerably during and after World War 2 but that didn't work its way into civil aviation for some time.  I suspect that a lot of this had to do with people getting so good with celestial navigation, dead reckoning, charts, compasses, and so on that they didn't see a need for anything else.  These methods work so well that we are seeing the US military training more people in them.  Helpful in case someone launches missiles at your satellites.  But I digress.
When it comes to the decision to give up the search there's only so long that people would expect to find survivors.  This would have been spring time in that part of the world and waiting for summer to continue the search would have made their work looking for the flight data recorder easier.  More than a week looking for survivors would likely be far longer than many would expect to find anyone alive.  Delays in the search for wreckage in the anticipation of better weather would be common then and now.
I also find myself amazed at times at the technical capabilities of aircraft and electronics from the time.  The problem is that this technology cost a lot of money then so it left people living in the 1970s with a world that to some looked more like the 1930s.  I wish I could recall where I heard this but it seems appropriate, "The future is now, it's just not evenly distributed."

Both the question and this answer seem to have missed the fact that GPS signals are only transmitted by satellites.  @mins explains it.

Small nitpick: civilian use of GPS with the accuracy needed for aircraft navigation didn't exist until the year 2000 or so. We were logging GPS tracks in gliding competitions already in 1995. An error of 50 meters is not a big deal when you are moving at 50m/s.

Did I correct the nitpick with my edit?

@MacGuffin Not really, and it's more than a nitpick.  For terrain/airspace avoidance, "close" isn't good enough, sure.  But for SAR, "close" is absolutely all you need.  Narrowing down to the nearest 1km is fine, and even 10km would give you a manageable search box.  To the nearest 100m, which was the "official" civilian accuracy with selective availability, puts you in direct line of sight.  The issue has never been the accuracy of positioning - it's always been the problem of getting that position back to SAR services.


text:
What is an "artificial decompression"?
Have anyone heard about "artificial decompression" ? And if yes, what does that mean ?
I know decompressions are usually classified as "explosive", "rapid" and "gradual" or "slow", but I've never heard about "artificial decompression" until a friend asked me about it...
Thanks !

Is there any example of the term being used besides your friend asking about it? May not be a real thing, or may be used in some very limited, niche context. Without some example of the term being used, it may be hard to answer this question very well.

Don't know for sure. I would interpret it as a decompression initiated on purpose, by pumping air out, for training or testing, as in an altitude chamber, where air will be sucked out slowly for hypoxia training, or quickly for explosive decompression training.

What’s the context/source?

Ralph, John, and Tedder: thanks for your comments... I'm currently trying to gather more informations/context about this "procedure"... I will keep you posted ! Thanks

It turned out that the term "artificial decompression" was a one-off encountered in a general article mentioning a case where the PIC decided to intentionally induce a decompression (using the cockpit system controls) with the intent to surprise and subsequently subdue some hijackers ( it is unknown if this is fictional...).
After additional research, I couldn't find any other usage of the term.
Thank You very much for your on point help (Ralph, John & Tedder) !

I might quibble with the original author & suggest that this is more the case of an intentional depressurization that "artificial," but that's a tiny point. Thanks for the update on the source of the term in question!


text:
What is meant when "flying/operating below Controlled Airspace"?
I'm currently studying for my PPL(A) and I've heard this phrase a few times now:

The QNH must be used for flight below the Transition Altitude when flying below Controlled Airspace

RPS should not be used when operating below Controlled Airspace.

Does this mean, you are flying in uncontrolled airspace (class F/G) with Class A-E above you?
So my question is can you have stacked airspaces -- multiple airspaces above a single point?

It seems you're in the UK, and there are 5 different types of airspace (A, C, D, E and G), each of which have different rules about clearances required, minimum visibility etc.

As you have noticed, the airspace above a given point does not have to belong to a single class, but there can be several layers on top of each other. Very common are e.g. the "inverted wedding cakes" of class C airspace above and around airports.
This picture from Germany shows it pretty clearly, the general idea should be the same for the UK:

Most airspace at low altitudes is uncontrolled G except at airports, above that is class E, and only at high altitudes, where IFR traffic (airliners) is predominant, do you have controlled airspace (class C) again. In other countries, this may be class A with no VFR traffic whatsoever allowed (e.g. in the US).
In the vicinity of airports you have the control zone (D) and above that, horizontally expanding, different layers of class C airspace, where IFR traffic departs or approaches the airport (the "inverted wedding cake" I referred to).
I am a little surprised that this is not part of what you are studying, but it may depend on the order in which you approach the different subjects.


text:
Why don’t fighter jets use symmetrical airfoils?
Won’t they be more manoeuvrable in dogfights?

Please give us an idea why you think that a symmetrical airfoil would be more maneuverable.  (Decades of engineering, test, and real world trial by fire has gone into current designs.)

It can produce lift when flown upside down. And are mostly used by stunt planes.

Do you have any evidence that fighter aircraft do NOT use symmetrical airfoils?

Fighters don't really need or want to fly at negative Gs for any sustained amount of time.  There is no tactical reason to do so, and it is very uncomfortable on the human body.
A short duration negative G bunt may be employed effectively as a defensive maneuver, but overall a fighter will always keep positive Gs on the airplane.  The body can tolerate many more positive Gs, which results in better turn performance, plus you can actually see in the direction you are turning!
Therefore it just makes sense to optimize the airfoil for best turn performance at positive G loading.  Aerobatic aircraft spend a lot more time at negative Gs so it makes some sense to help them out with a more symmetrical shape.

Does it mean that there’s no tactical meaning in fly upside down constantly and with asymmetric airfoils will make jet have a smaller turn radius with just the movement of the tail foil? But this brings  up a question for me, is there any more ice for symmetrical airfoils as wings?

Correct, no tactical reason to fly upside down constantly.  To the extent that turn radius is created by lift, then yes, an airfoil with a better coefficient of lift will have a smaller turn radius.  (There are some caveats I am probably missing with this generalization, and maybe one of the aero engineering pros can explain better.)  I can't see any connection between symmetry and susceptibility to ice accumulation.

Sorry for the typo, I meant is there any more uses for symmetrical airfoils?

Well, when you want the forces to be symmetrical, like on a vertical tail, wing strut fairing, etc.  For wings?  The only advantage I see is enhancing the ability to fly inverted.

Also you can't fire missiles from underwing and ventral stores at negative Gs, and only few fighters even have wingtip rails and there can obviously be only two of those.

Another advantage of symmetrical arifoils is, that curvature of the airfoil also introduces higher wavedrag. So symmetrical Airfoils have "usually" lower Drag at supersonic flight.

What makes you think they don't.  As the old saying goes "with enough thrust pigs fly just fine"  To be serious, fighters also have to land and a little asymmetry would help at lower speeds, although I don't expect they use much, and it may only be a portion of the wing.  The F-16 lands around 155 kts, so the wings are probably pretty symmetrical.  Keep in mind that modern fighters fly at supersonic speeds and high altitudes and there are always going to be trade-offs.

Pretty symmetrical yep, but not quite!

I concur they are not.  And any trend towards symmetry would be to optimize performance at the air speeds, altitudes, and positive G loading they are designed for, and NOT a compromise to squeak better inverted lift out of the wing…


text:
On fighter jets (e.g. F-16), do the leading edge flaps extend above the retracted position, as well as the more typical down extension?
Do they go both up and down (with respect to a retracted position in the middle) on different fighter jets?

https://www.f-16.net/forum/viewtopic.php?t=11863

DV for lack of clarity and thought put into the question.  (I.e. if something is moveable and has more than one position, why would you think it might NOT move?  Barring a malfunction…)

@ymb1, OK, I understand that F-16 LEFs are a maneuvering aide, but now instead of reading like "does the landing gear go up and down?" it reads like "after the landing gear fully retracts, does it go even further up?"  Better might be rephrasing to ask about movement around a default neutral, or cruise position?  Anyway, I don't feel compelled to guess the intent or do Chickeny Chickens' work for them...

Interesting topic, but I think the question can be more valuable if it also asks the 'why' question.

I can answer on the F-16 :)
The general system description tells us that the Leading Edge Flaps may be positioned from 2 degrees (1 inch) up to 25 degrees (12-1/2 inches) down.
I assume it is similar on the F-22 and F-35, since the Leading Edge Flap subsystem provides high lift for takeoff and landing and optimizes performance in each flight
phase.

Will the LEF going up have any functions?

The LEF system is designed to optimize wing airflow. It provides special functions in the takeoff and landing configurations.

LEF 2 degrees up primarily has use during takeoff.
When there's weight on wheels (aircraft on ground), the LEFs will be in the 2 degree up position.

At subsonic speeds, the LEF's move from 2 degrees up to 25 degrees down as a function of mach number, Angle Of Attack, and altitude. This is an automatic operation that significantly reduces buffet and drag and improves high AOA directional stability.

Here is a video of the first F-16 flight test: https://www.youtube.com/watch?v=UR-48Kri0Tw
I know the description says it was supposed to be a high speed taxi, but in reality it was supposed to fly, to test low speed stability. You can see here that the leading edge flaps are all the way down, and that the aircraft is super unstable in low speed flight.

If the speed is above 1.0 Mach the LEF 's and TEF 's are up 2degrees , not only on the runaway


text:
How are ARINC 429 BCD dd:mm:yy labels encoded?
Label 260 (Date) has a dd:mm:yr format, which requires 6 characters. How is this label typically coded? Here is my best guess based on the range of each digit:

Bit #
Another header

1-8
Label (260)

9
SDI

10
SDI

11
digit #6 LSB

12
0/1

13
0/1

14
digit #6 MSB

15
digit #5 LSB

16
0/1

17
0/1

18
digit #5 MSB

19
digit #4 LSB

20
0/1

21
0/1

22
digit #4 MSB

23
digit #3

24
digit #2 LSB

25
0/1

26
0/1

27
digit #2 MSB

28
digit #1 LSB

29
digit #1 MSB

30
SSM

31
SSM

32
Parity

Is this correct?

You are correct.
There is a direct example for label 260 in Table 6-18 of ARINC 429 Part 1 dated May 17th, 2004 that identifies the following bit ranges for the corresponding digit:
Bits 29:28 - Day x10
Bits 27:24 - Day x1
Bit  23    - Month x10
Bits 22:19 - Month x1
Bits 18:15 - Year x10
Bits 14:11 - Year x1


text:
What is the format for standard ARINC 429 labels with 20 sig bits?
Certain standard labels in the ARINC 429 specification have 20 significant bits. For example, Label 110 (GNSS Latitude) has a range of +/- 180 degrees, with a resolution of .000172 degrees. In order to accomplish this, how is the word formatted? Does the data run into the SDI field like so?

Bit #
Another header

1-8
Label (110)

9
0.000171661377

10
0.0003433227539

11
0.0006866455078

12
0.001373291016

13
0.002746582031

14
0.005493164063

15
0.01098632813

16
0.02197265625

17
0.0439453125

18
0.087890625

19
0.17578125

20
0.3515625

21
0.703125

22
1.40625

23
2.8125

24
5.625

25
11.25

26
22.5

27
45

28
90

29
Sign (0/1)

30
SSM

31
SSM

32
Parity

Or does the sign bit move to bit 31, replacing the SSM instead?

The extra bits of precision would use the SDI bits as you've suggested.
From ARINC 429 Part 1 dated May 17th 2004

2.1.4 Source/Destination Identifier

Bit Numbers 9 and 10 of numeric data words should be
reserved for a data source/destination identification
function. They are not available for this function in
alpha/numeric (ISO Alphabet Number 5) data words (see
Section 2.3.1.3 of this document) or when the resolution
needed for numeric (BNR/BCD) data necessitates their use
of valid data.


text:
What could cause an air data computer interfaced via A429 to only display integer values?
I'm working with a Shadin 2000 air data computer interfaced via ARINC 429 to an Avidyne IFD 550. For some reason, the airspeed tape is flipping between discreet values, and not gradually increasing/decreasing. This makes the readout appear very ratchety or jumpy.
I'm by no means an expert on troubleshooting these kinds of problems. What could be causing this?

Check the message format expected by the 550.  Verify That the 2000 is encoding in that format and verify that the expected data is being sent.  You’ll need a bus analyzer.

I don’t see the 2000 on this list: https://pilotsupport.avidyne.com/kb/article/433-ifd5xx-4xx-compatible-equipment/

Interesting- the configuration setting for it is shown in the Installation Manual: https://imgur.com/a/KVT7DM4

Well, good. I wouldn’t trust info you randomly find on the internet ;-)

Not sure what rate the IFD 550 expects the transmit rate to be, but from what I can find on the Shadin 2000, it's label transmit rate is configured by a switch position and can vary from 50,100, or 200 ms, which longer periods could cause a jumpy display if it isn't filtering the received label at all.


text:
Hexacopter Vn diagram/ flight envelope/ operational envelope
I am currently intern at a company. They are making agriculture hexacopter, now there is a confusion that does the hexacopter or multicopter have a V n diagram if yes how to make one what's the correct way, and what is the operational and flight envelope for multicopter? So confusion any help

There's no expert and/or senior engineer in that company you can ask about these subjects? Or is it a start-up that has never done helicopters before?

Vn diagrams for multicopters are a bit pointless. A normal flight envelope is used to convey to the pilot where the limits are and why they are at that specific point. This is often important, as you might have several limits which come to play, such as structural limits, stall limits, power limits and so on. Keeping track of all these limitations in order not to damage the aircraft for example, is a critical task for a pilot hence the flight envelope diagram.
For a multicopter however, all of this is not important because they have typically only one very uncritical limit: The power. Having said that, I speculate that the Vn diagram of a multicopter looks similar to the following picture:

Please be aware, that I did not calculate this envelope. Therefore I am not exactly sure if the power limit is a straight line, but it should at least resemble this graph.
I hope this answers your question at least in parts.

Okay got the point, so i guess there is no calculation or diagram that depicts these limits, i saw velocity height diagram for helicopter thought that is similar for multicopter, then how the operational envelope for a multicopter is decided, lets say i have to design a hexacopter drone, how do i calculate its operational/flight envelope. any way to do this ?